Nose wheel steering system for aircraft



H. P. KuPlEc ETAL 2,657,883

NOSE WHEEL STEERING SYSTEM FOR AIRCRAFT Nov. 3, 1953 Filed June 2l, 19514 Sheets-Sheet l Nov. 3, 1953 H.y P. KUPIEC ET AL NOSE WHEEL STEERINGSYSTEM FOR AIRCRAFT 4 Sheets-Sheet 2 Filed June 21, i951 Zamw /rrMA/EKSNOV 3, 1953 H. P. KUPIEC ET A1. 2,657,883

NOSE WHEEL STEERING SYSTEM FOR AIRCRAFT 4 Sheets-Sheet 3 Filed June 21,1951 w .MW

Nov. 3, 1953 H. P. KUPlEc ET AL NOSE WHEEL STEERING SYSTEM FOR AIRCRAFT4 sheds-sheet 4 Filed June 2l, 1951 Xxx( Patented Nov. 3, 1953 NOSEWHEEL STEERING SYSTEM FOR AIRCRAFT Harry P. Kupiec, Paramus, and EverettG.

Gravenhorst, Hasbrouck Heights, N. J., assignors to Air Associate s,Inc., Teterboro, N. J., a

corporation of New Jersey Application June 21, 1951, Serial No. 232,8387 Claims. (Cl. 244-50) This invention relates to an hydraulic system forturning the nose wheel of aircraft for directing the aircraft whentraveling on land.

The invention is directed to an hydraulic system in which areciprocatory pressure responsive device is operatively connected withthe nose Wheel steering axle of the aircraft and with a control valvearranged inthe system for admitting hydraulic fluid to either end of thedevice for turning the steering axle in accordance with the movement ofthe steering wheel of the aircraft.

Another obiect of the invention is to provide an hydraulic system whichis constructed and arranged to provide a slow turning movement of thenose wheel steering axle when the same is initially turned and a morerapid turning movenient thereof after the initial movement.

Still another object of the invention is to provide an hydraulic systemwhich reduces or dampens shimmying action of the nose wheel steeringaxle.

Still another object of the invention is to provide a system havingmeans for shutting off the ow of the hydraulic fluid to the operationalparts of the system when the nose wheel is out of engagement with theground.

Another object of the invention is to provide an hydraulic system ofsaid character in which the aircraft may be turned or manipulated onland by utilizing the power of the engines, the application of thebrakes to the main wheels of the landing gear, the manipulation of thecontrol surfaces of the aircraft or a combination of the use of theseparts without employing the hydraulic system for moving the nose Wheel.When turning or maneuvering the aircraft on land in this manner, thenose Wheel will follow the turning of the aircraft and the pressureresponsive device will move in accordance with the turning of the nosewheel. rI'he movement of the pressure responsive device will increasethe pressure of the hydraulic fluid in one end thereof and cause areduction in the pressure of the hydraulic fluid in the opposite end.The increased pressure in one end of the pressure responsive device willproduce a flow of the fluid from said end and in order to provide forthe flow of fluid into the opposite end thereof, the present inventionprovides check. valves interposed in the system between the fluid returnline and the high pressure lines leading from the control valve to theopposite ends of the pressure responsive device. By this arrangement,voiding in the reduced pressure end of the pressure responsive device isprevented under all conditions of steering of the aircraft while anominal value of back pressure in the return line can be used.

Still another object of the invention is to provide a system of saidcharacter which operates on standard hydraulic pressure utilized inaircraft and the like and which will operate on pressures of 560 to3,000 lbs. per square inch and which relieves the tension on thesteering wheel and renders the same sensitive in operation.

With the foregoing and other objects in View, reference is now made tothe following drawings and accompanying specification in which thepreferred embodiment of the invention is illustrated.

ln the drawings:

Fig. 1 is a diagrammatic view of an hydraulic system constructed inaccordance with the in- Vention.

Fig. 2 is an enlarged fragmentary sectional View of the steer cylinderand rod taken approximately on line 2-2 of Fig. 1.

Fig. 3 is a side view of the link pivotally connected with the cylinder,

Fig. 4 is an enlarged longitudinal sectional view of the steer valvetaken approximately on line 'fl-4 of Fig. 1.

Fig. 5 is a cross-sectional View taken approximately on line 5 5 of Fig.4.

Fig. 6 is a longitudinal sectional View taken approximately on line 6 6of Fig. 4.

Fig. 7 is an enlarged sectional View through the accumulator, takenapproximately on line 'l-'l of Fig. 1.

Fig. 8 is an end view of the shut-off valve.

Fig. 9 is an enlarged longitudinal sectional view taken approximately online 9-9 of Fig. 8.

Fig. 10 is a side View of the relief valve.

Fig. 11 is an enlarged longitudinal sectional View taken approximatelyon line lI-ll of Fig. 10.y

Fig. 12 is a schematic side view of a nose wheel column in extendedposition on an aircraft and showing the location of the pressureresponsive device for turning the nose wheel.

Referring to the drawings by characters of reference, the systemincludes an hydraulic pressure responsive device lil operativelyconnected With the nose wheel column A of an aircraft and the like forturning the nose wheel E for maneuvering the aircraft on land, a controlvalve Il operatively connected with the steering wheel E of the aircraftfor admitting hydraulic fluid to the pressure responsive device throughconduits I2 and i3 in response to the movement of the steer- .openingsing wheel, a shut-.off valve I5 for shutting off hydraulic fluid to thesystem when the nose wheel is elevated, an accumulator I6 and a reliefvalve |1 connected in the system with the return or low pressure conduitIB, and two check valves I9 and 20 connected in the system between thelow pressure conduit I8 and the conduits I2 and I3 respectively. Theconduits |2 and I3 are respectively connected with service ports 2| and22 of the control valve and with the ports 23 and 24 at the oppositeends of the pressure responsive device I8.

The pressure responsive device I consists of a reciprocatory cylinder 26which is mounted for longitudinal reciprocatory movement on a. rod 21fixed at its ends in apertures 28 and 29 respectively in oppositelydisposed brackets 38. The said brackets are secured by bolts 3| tobrackets 32 affixed to the fixed upper portion C of the nose wheelcolumn of the aircraft to dispose the rod 21 in horizontal relation. Therod 21 is formed with a head 33 located medially thereof which snuglyflts the inner periphery of the cylinder 26 while the opposite ends ofthe rod snugly protrude through openings 34 and 36 in the end wells 36Vand 31 of the cylinder for sliding movement of the cylinder on the rod.The ports 23 and 24 are formed in the end walls of the cylinder foradmitting hydraulic fluid to either end thereof on opposite sides of thehead 33 for movement of the cylinder in either direction longitudinallyof said rod. The end wall 36 of the cylinder is formed with a slotteddepending Dortion 39 for receiving the bifurcated end of a link 4|pivoted on a bearing pin 42 disposed in aligned openings 40. The link 4|is arranged for swinging movement in a plane disposed in parallelrelation with the longitudinal axis of the cylinder and is provided witha bearing opening 43 in which is pivoted the vertical pin 44 of abracket F aflxed to the lower portion D of the nose wheel column. Thesaid lower portion D of the nose wheel column constitutes the steeringaxle of the nose wheel E and is supported for turning movement in thelower end of the upper portion C of the nose wheel column affixed in anydesired manner, such as by the struts H to the aircraft indicatedgenerally by the reference character G, The head 33 is provided with anopening 45 which is of a size to permit of the gradual flow of fluidfrom the high pressure side of the head to the low pressure side thereoffor a purpose to be hereinafter described.

The control valve I| is also provided with pressure and return ports 48and 49, which together with the service ports 2| and 22 open into alongitudinally extending steel sleeve I tightly fitting and extendingthe full length of the bore 58 of the valve body. The sleeve 5| isprovided with openings 52 and 53 disposed in registry with the pressureand return ports 43 and 49 and in right angular relation to saidopenings 52 and 53 the sleeve is formed with small openings 54 and 53disposed in registry with the service ports 2| and 22 respectively.Adjacent said openings 54 and 55 the said sleeve is formed with aplurality of transversely aligned relatively small 56 and 51 disposed inregistry with the g 2| and 22 respectively, the openings 56 beingdisposed to the left of the openings 64 and the openings 51 beingdisposed to the right of the openings 55 as shown in Figs. 5 and 6 ofthe drawings.

A plunger 59 is mounted for longitudinal reciprocatory movement in thesleeve for regulat- Bervice ports ing the flow of the hydraulic fluidfrom the fluid pressure port 48 in either direction through said serviceports 2| and 22. and to the cylinder 26 through the conduits I2 and I3and the discharge of the return flow through the return port 49. Forthis purpose, the plunger 59 is cut away or reduced in diameter atlongitudinally spaced portions 60, 6| and 62 providing circumferentiallands 63 and 64 which are provided with packing rings 65 and 66 toprevent the flow of fluid between the said lands and the inner peripheryof the sleeve 5|. The said reduced portions also provide circumferentiallands 61 and 68 disposed in spaced relation between the lands 63 and 64and which are adapted to regulate the flow of the hydraulic fluidthrough the openings 54 and 56 leading to the service port 2| andthrough the openings 55 and 51 leading to the service port 22. Thesleeve 5| is provided with openings 10 and 1| which communicate with theannular recesses 12 and 13 respectively provided by the reduced portions68 and 62 of the plunger and which also communicate with alongitudinally extending slot 14 formed in the outer periphery of thesleeve whereby the hydraulic fluid from the service port 2| isdischarged through the opening 18, slot 14. opening 1| and thencethrough the return port 49 while the hydraulic fluid from the serviceport 22 flows directly from the annular recess 13 through the returnport 49.

The plunger 59 is provided with a tensioning device indicated generallyby the refernce character 16 which normally retains the plunger inposition with the lands 61 and 68 disposed in partially coveringrelation with the openings 54 and 55. The tensioning device 16 includesa housing 11 aiiixed to one end of the control valve with one end of theplunger projecting into said housing. Located within the housing 11 areflanged tubular members 38 and 8| arranged on the plunger 59 with theflanges 32 and 33 thereof respectively disposed against the outer end ofthe housing and against a shoulder 19 located at the inner end of thereduced portion of the plunger. A coiled contractile spring 84 isinterposed between said anges which spring tensions the plunger tonormally dispose the lands 61 and 68 in partially covering relation withsaid openings as hereinbefore set forth. A lock nut 18 arranged on athreaded stud 85 is adapted to provide the desired tension of the spring84.

The plunger 59 protrudes through the control valve at the opposite endfrom the tensioning device and mounted on the protruding end thereof isa bifurcated extension 35 between the turca.- tions of which a link 86is pivoted on the pivot pin 81. The link 86 is aillxed at its oppositeend to the steering column 38 of the steering wheel B whereby thesteering wheel may be turned in one direction to move the plunger so asto permit of the ow of the uid through the pressure port 2| with thereturn flowing through the pressure port 22, and may be turned in theopposite direction to move the plunger so as to permit of the ow of thefluid through the pressure port 22 and the return flow through thepressure port 2|. The valve is provided with an apertured lug 69 formounting the same on a fixed part of the aircraft for pivotal swingingmovement on a pin extending through the apertured lug to permit ofrocking movement of the valve with the arcuate movement of the lever 86about the steering column 36.

The control valve l is connected with the shutoff valve |5 by a fluidpressure conduit 90 leading from the pressure outlet port 9| of theshut-olf valve to the pressure port 48 of the control valve. The returnport 49 of the control valve is connected with the low pressure conduitIS by a conduit 92 and with the return port 93 of the shut-01T valve.The shut-off Valve is provided with a pressure port 94 which isconnected in the system with a pressure pump (not shown).

The shut-off valve I5 is provided with a plunger 96 mounted forreciprocatory movement in a longitudinally extending bore 91 openingthrough the opposite ends thereof and which is closed at one end by aplate 98 with the plunger 96 protruding through the opposite end andhaving a headed stud 99 threadedly engaged in the protruding end foradjusting the head toward and away from the end of the plunger. The saidplunger is formed with a cylindrical recess |0| which is normallydisposed in registry with the pressure outlet port 9| and the pressuresupply port 94 by means of a coil spring |02 tensioned between the innerend of the plunger and a flanged stem |93 fitted in the bore 91 inabutting engagement with the plate 66. The said valve is formed with aduct |04 extending diagonally from the return port 93 to a recess |05formed in the periphery of the bore 91 at the inner end of the plunger96. The said valve is also formed with a duct |06 extending diagonallyfrom the outlet port 9| to the bore 91 and which is normally closed bythe plunger 96. The valve is so located that the headed end |00 isadapted to be engaged by the nose wheel or supporting part when the nosewheel is out of engagement with the ground to thereby cam the plunger 96inwardly against the tension of the spring |02 to move the recessedportion |0| thereof into registry with the duct |06 and recess |05 toshut off the pressure supply port 92 and the outlet port 9| whereby thepressure supply of the hydraulic fluid is shut oli to the system whilethe outlet port 9| is open to the return port 93.

rIhe plunger 96 of the shut-oir valve |5 is formed with a peripheralrecess |06 which communicates through an opening |09 in the plunger witha longitudinally extending bore ||0 opening through the inner endthereof. By this construction fluid ilowing from the recess |0| betweenthe bore 91 and the periphery of the plunger 96 escapes through therecess |08 and thence into the bore |0 and is discharged through theduct |04 and return 93. A flexible rubber bellows ||2 is secured at itsinner end in surrounding relation with the outer end of the body of thevalve and the outer end of the plunger as illustrated in Fig. 8 of thedrawings.

The accumulator I6 may be of any desired type such as a spring loadedtype provided with a coil spring H interposed in surrounding relationwith the guide rod ||5 and tensioned against the upper end I6 of theaccumulator and the piston head |1 secured to the lower end of the guiderod.

The relief valve |1 is of a type adapted to be set to provide thedesired pressure in the return conduit |8 such as 200 pounds per squareinch when utilizing a pressure of 1,500 pounds per square inch in thefluid pressure conduit 90. The relief valve |1 is provided with apressure port |20 and a return port |2| which ports communicate with abore |23 extending longitudinally of said valve. The bore |23 is closedat its lower end by a plug |24 and at its upper end by a screw cap |25which is threadedly engaged in the threaded opening |26 in the upper endof the valve for regulating the pressure of the coil spring |28 againstthe piston |29. The piston |29 bears against a poppet |30 which ismounted for reciprocatory movement'in a sleeve |3| fitted at its lowerend in the plug |24. The sleeve |3| is formed with a plurality ofcircumferentially spaced openings |33 for admitting fluid from thepressure port |20 into the passageway in said sleeve. The upper end ofthe sleeve forms a valve seat for the conical upper end portion |32 ofthe poppet for shutting off the flow of fluid from the pressure port |20to the return port |2|. The return port |2| is connected by a conduit|34 with the low pressure side of the pressure pump (not shown).

When the aircraft is on the ground both ends of the cylinder 26 of thepressure responsive device |0 are open to the low pressure conduit |8through the control valve Turning the steering wheel B in a clockwisedirection opens the service port 22 to the now of fluid from thepressure supply conduit to the left hand end of the cylinder formovement thereof to the right to thereby effect counterclockwise turningmovement of the lower portion D of the nose wheel column with aconsequent turning of the nose wheel. Turning of the steering wheel B asdescribed also opens the service port 2| to the low pressure conduit |8for the ilow of iiuid from the right hand end of the cylinder to thereturn conduit I8. Turning of the steering wheel B in a counterclockwisedirection similarly effects turning ofA the lower portion D of the noseWheel column in a clockwise direction with a consequent turning of thenose wheel.

The initial turning movement of the steering wheel B functions to openthe small openings 54 and 55 which permits of the flow of a smallquantity of the fluid through the service ports. This imparts a slowinitial movement of the cylinder and consequently a slow initialmovement of the nose wheel. Further turning of the steering wheel Bmoves the lands 61 and 68 to fully open the series of openings 56 and51. This functions to permit of the full flow of the fluid to and fromthe cylinder to thereby impart a more rapid turning movement to the nosewheel.

The restricted opening 40 in the head 33 of the pressure responsivedevice |0 permits of the dow of fluid from the high pressure side of thehead to the low pressure side thereof. This functions to produce acushioning action or a smooth acceleration of the cylinder to therebydampen or retard shimmying action of the nose wheel.

The check valve 20 is arranged to permit of the flow of fluid from thelow pressure conduit |8 through the conduit |3 and to the left hand endof the cylinder 26 when the cylinder is moved to the left by the turningofthe nose wheel E by the use of the engines of the aircraft, theapplication of the brakes to the main wheels of the landing gearthereof, the manipulation of the control surfaces or a combination ofthe use of these parts. When turning or maneuvering the aircraft on landin this manner, without the application of hydraulic pressure in thesystem, the nose wheel will follow the turning of the aircraft and thecylinder 25 will move with the turning of the nose wheel. This movementof the cylinder to the left will increase the pressure of the fluid inthe right hand end of the cylinder with a consequent reduction of thepressure in the left hand end thereof. The increased pressure in theright hand end of the cylinder will force fluid to ilow from said endand .through the control valve I I to the low pressure conduit I8.'Since the opening 55 in the control valve II is relatively small, thesame will not permit of suilicient ow of fluid into the left hand end ofthe cylinder to fill up the space therein due to the movement of thecylinder to the left. The .check valve 2U vis provided for this purposewhich permits of the flow of fluid from the low pressure conduit I8 tothe left hand end of the cylinder. This prevents voiding of the fluid inthe left hand end thereof while maintaining a normal pressure such as200 pounds per square inch in the low pressure conduit I8 and at thesame time utilizing a pressure of 1,500 pounds per square inch in thepressure supply line. The check valve I9 functions similarly to permitof the flow of fluid from the low pressure conduit I8 to the right handend of the cylinder when the cylinder is moved to the right by theturning of the nose wheel by other means than the hydraulic system.

There is thus provided an hydraulic system by which the nose wheel maybe turned for directing the aircraft when traveling on land and whichsystem permits of the turning of the aircraft on land by its own powerand the manipulation of its controls without `the use of the hydraulicpressure and without the build-up of excessive pressure in the hydraulicsystem.

It is to be understood that the conduits I2 and I3 connected between thecylinder 26 and the control valve II are flexible to permit ofreciprocatory movement of the cylinder 26 and swinging movement of thecontrol valve II on the pivotal connection extending through theapertured lug 89. The conduits 90 and 92 are also flexible to permit ofthe pivotal swinging of the control valve II.

What is claimed is:

l. In an hydraulic system for turning the guiding wheel of an aircraftfor turning the aircraft when traveling on land, an upwardly extendingcolumn including an upper portion affixed to the aircraft and a lowerportion supported by the upper portion for turning movement and on whichthe guiding wheel is mounted, a pressure responsive device including areciprocatory cylinder, a rod afllxed to the upper portion of saidcolumn and having a head, said cylinder being mounted on said rod forreciprocatory movement thereon and with the head located within thecylinder, a link pivotally connected to said cylinder and pivotallyconnected to the lower portion of said column for turning the same withthe movement of the cylinder, a valve in said system connected with ahigh pressure supply conduit and a low pressure return conduit and withtwo service conduits extending from said valve to and opening into theends of the cylinder, a plunger mounted for reciprocatory movement insaid valve, a steering member, and means operatively connecting saidsteering member to said plunger for moving the plunger to thereby opensaid valve for the ow of hydraulic fluid from the valve into one lend ofthe cylinder and the ilow of hydraulic fluid from the other end of thecylinder through said valve for imparting movement to the cylinder.

2. In an hydraulic system for turning the guiding wheel of an aircraftfor turning the aircraft when traveling on land, an upwardly extendingcolumn including an upper portion affixed to the aircraft and a lowerportion supported by the upper portion for turning movement and on whichthe guiding wheel is mounted, a pressure responsive device including areciprocatory cylinder, a. rod afxed to the upper portion of said columnand having a head, said cylinder being mounted on said rod forreciprocatory movement thereon and with the head located within thecylinder, a link pivotally connected to said cylinder and pivotallyconnected to the lower portion of said column for turning the same withthe movement of the cylinder, a valve in said system having portsconnected with a high pressure supply conduit and a low pressure returnconduit and two service ports connected with service conduits extendingto and opening into the ends of the cylinder, a plunger mounted forreciprocatory movement in said valve, means tensioning said plunger forresiliently maintaining the same with the service ports in partiallyopen relation, a steering member, means operatively connecting saidsteering member to said plunger for moving the plunger to thereby opensaid valve for the flow of hydraulic fluid from the high pressure supplyconduit into one end of the'cylinder and the flow of hydraulic fluidfrom the other end of the cylinder through said valve and into thereturn conduit, and check valves arranged in by-pass conduits extendingfrom said low pressure return conduit to said service conduitsrespectively to permit of the flow of fluid from the low pressure returnconduit to either end of the cylinder to compensate for the movement ofthe cylinder when the aircraft is moved on land without the use of thehydraulic system.

3. In an hydraulic system for turning the guiding wheel of an aircraftfor turning the aircraft when traveling on land, an upwardly extendingcolumn including an upper portion afllxed to the aircraft and a lowerportion supported by the upper portion for turning movement and on whichthe guiding wheel is mounted, a pressure responsive device including areciprocatory cylinder, a rod alxed to the upper portion of said columnand having a head, said cylinder being mounted on said rod forreciprocatory movement thereon and with the head located within thecylinder, a link pivotally connected to said cylinder and pivotallyconnected to the lower portion of said column for turning the same withthe movement of the cylinder, a valve in said system having portsconnected with a high pressure supply conduit and a low pressure returnconduit and two service ports connected with service conduits extendingto and opening into the ends of the cylinder, a plunger mounted forreciprocatory movement in said valve, means tensioning said plunger forresiliently maintaining the same with the service ports in partiallyopen relation, a steering member, means operatively connecting saidsteering member to said plunger for moving the plunger to thereby opensaid valve for the flow of hydraulic fluid from the high pressure supplyconduit into one end of the cylinder and the flow of hydraulic uid fromthe other end of the cylinder through said valve and into the returnconduit, and check valves arranged in by-pass conduits extending fromsaid low pressure return conduit to said service conduits respectivelyto permit of the flow of fluid from the low pressure return conduit toeither end of the cylinder to compensate for the movement of saidreciprocatory member when the aircraft is moved on land without the useof the hydraulic system.

4. In an hydraulic system for turning an aircraft when traveling onland, a guiding wheel mounted on a transverse axle, an upwardly exaccusatending column aiixed to the aircraft for swivel turning movement, saidtransverse axle being mounted in the lower end of said column forturning movement therewith, a pressure responsive device including areciprocatory cylinder, a link connected with said cylinder and saidcolumn for pivotal swinging movement for turning the column with themovement of the cylinder, a valve in said system connected with a highpressure supply conduit and a low pressure return conduit and with twoservice conduits extending from said valve to and opening into the endsof the cylinder, a plunger mounted for reciprocatory movement in saidvalve, a steering` member, and means operatively connecting saidsteering member to said plunger for moving the plunger to thereby opensaid valve for the ilow of hydraulic iluid from the Valve into one endof the cylinder and the ow of hydraulic iluid from the other end of thecylinder through said valve for imparting movement to the cylinder.

5. In an hydraulic system for turning the guiding wheel of an aircraftlfor turning the aircraft when traveling on land, an upwardly extendingcolumn including an upper portion aiixed to the aircraft and a lowerportion supported by the upper portion for turning movement and on whichthe guiding wheel is mounted, a pressure responsive device including areciprocatory cylinder, a rod aiiixed to the upper portion of saidcolumn and having a head, said cylinder being mounted on said rod forreciprocatory movement thereon and with the head located Within thecylinder, a link pvotally connected to said cylinder and pivotallyconnected to the lower portion of said column for turning the same withthe movement of the cylinder, a valve in said system having portsconnected with a high pressure supply conduit and a low pressure returnconduit and two service ports connected with service conduits extendingto and opening into the ends of the cylinder, a plunger mounted forreciprocatory movement in said valve, means tensioning said plunger forresiliently maintaining the same with the service ports in partiallyopen relation, a steering member, means operatively connecting saidsteering member to said plunger for moving the plunger to thereby opensaid valve for the now of hydraulic iiuid from the high pressure supplyconduit into one end of the cylinder and the ow of hydraulic fluid fromthe other end of the cylinder through said valve and into the returnconduit. a shut-off valve interposed in the high pressure supplyconduit, said shutoff valve having a reciprocatory plunger for shutting01T the ow of the iluid through the valve, means tensioning said plungerfor normally maintaining the same with the valve in open relation, andsaid plunger protruding through one end of the valve and having a headadapted to be engaged by an operating part moving with the guiding wheelfor moving the plunger inwardly to thereby shut off the flow of iluidwhen the guiding wheel is elevated from the ground.

6. In an hydraulic system for turning an aircraft When traveling onland, a guiding wheel mounted on a transverse axle, an upwardlyextending column aflixed to the aircraft for swivel turning movement,said transverse axle being mounted in the lower end of said column forturning movement therewith, a pressure responsive device including areciprocatory cylinder, a

connected with said cylinder and scid co1- umn for pivotal swingingmovement for turning' the column with the movement of the cylinder, avalve in said system connected with a high pressure supply conduit and alow pressure return conduit and with two service conduits extending fromsaid valve to and opening into the ends of the cylinder, a plungermounted for reciprocatory movement in said valve, a steering member,means operatively connecting said steering member to said plunger formoving the plunger to thereby open said Valve for the ilow oi hydrauliciluid from the valve into one end of the cylinder and the ilow ofhydraulic fluid from the other end of the cylinder through said valvefor imparting movement to the cylinder, a shut-oil valve interposed inthe high pressure supply conduit and having a plunger provided with ahead protrudingl through one end of the valve and adapted to be engagedby an operating part moving with the guiding wheel for moving theplunger inwardly to thereby shut oir the flow of iluid when the guidingwheel is elevated from the ground.

7. In an hydraulic system for turning an aircraft When traveling onland, a guiding Wheel mounted on a transverse axle, an upwardlyextending column aiiixed to the aircraft for swivel turning movement,said transverse axle being mounted in the lower end of said column forturning movement therewith, a pressure responsive device including kareciprocatory cylinder, a link connected with said cylinder and saidcolumn for pivotal swinging movement for turning the column with themovement of the cylinder, a valve in said system connected with a highpressure supply conduit and a low pressure return conduit and with twoservice conduits extending from said valve to and opening into the endsof the cylinder, a, plunger mounted for reciprocatory movement in saidvalve, a steering member, means operatively connecting said steeringmember to said plunger for moving the plunger to thereby open said valvefor the flow of hydraulic iluid from the valve into one end of thecylinder and the iiow of hydraulic iiuid from the other end of thecylinder through said valve for imparting movement to the cylinder, andcheck valves arranged in by-pass conduits extending from said lowpressure return conduit to said service conduits respectively to permitof the now of iluid from the low pressure return conduit to either endof the cylinder to compensate for the movement of the cylinder when theaircraft is moved on land Without the use of the hydraulic system.

HARRY P. KUPIEC. EVERETT G. GRAVENHORST.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 548,289 Bonner Oct. 22, 1895 2,243,364 Trautman May 27, 19412,424,233 Greenough July 22, 1947 2,474,681 Lane June 28, 1949 2,506,093MacDui May 2, 1950 2,552,843 Clifton May 15, 1951 2,577,999 ChristensenDec. 11, 1951 FOREIGN PATENTS Number Country Date 629,649 France Aug. 1,1927

